The Assignee of the present application owns several patents pertaining to the pasteurization of shell eggs including for example Cox et al. U.S. Pat. No. 5,589,211, and Davidson U.S. Pat. No. 6,322,833, each of which is incorporated herein by reference. In general, commercialized pasteurization processes involve the use of a fluid pasteurization medium, such as heated water, heated oil, heated air or steam. In some systems, batches of shell eggs are submerged into a heated bath and moved sequentially from zone to zone in order to complete the pasteurization process. Other systems do not move the batches of eggs sequentially through the bath but hold each batch in place for the duration of the pasteurization process. Certain aspects of the present invention apply to both types of systems. In either case, the purpose of the process is to heat the entire mass of the egg such that the center of the egg yolk warms to an adequate temperature for a sufficient amount of time to pasteurize the egg and meet or exceed an accepted standard for reduction of Salmonella Enteriditis without cooking the egg. A 5 log reduction in salmonella is the regulated standard set by the FDA for a shell egg to be labeled as pasteurized. In some cases, it may be desirable to achieve at least a 7 log reduction or more. Also in some jurisdictions, a lower standard such as 2 or 3 log reduction may be acceptable. Pasteurization has been shown to kill other food born pathogens as well. After pasteurization, the eggs can optionally be coated with FDA approved food-grade wax or other sealant containing antibacterial properties to further protect the eggs from outside contaminants. After pasteurization and sealing, the exterior of the eggs are dried, cooled and packed for storage, preferably at or below 45° F. It is typical to label the pasteurized eggs as pasteurized.
Once pasteurized, the eggs are safe for consumption even if raw or partially cooked. It is still recommended, although not required by U.S. regulations, to refrigerate pasteurized eggs during shipment and storage in order to extend shelf-life and to maintain high egg quality and functionality. Conversely, unpasteurized eggs are required by U.S. regulations to be refrigerated because they are a potentially hazardous food which poses a recognized salmonella health risk. Pasteurized shell eggs, on the other hand, no longer carry significant quantities of salmonella because the pasteurization process destroys all or almost all of the bacteria.
Just as it is important to uniformly heat the entire mass of the egg to a given temperature for the required period of time, it is also important not to overheat the egg during the pasteurization process. Overheating can result in partial cooking or loss in the quality and functionality of the egg. There are many methods for measuring egg quality and functionality, see for instance the methods discussed in above incorporated U.S. Pat. No. 6,322,833. One of the most common functionality tests is the albumen functionality test which measures egg white quality in Haugh units. As an egg ages, the thick portion of the egg white tends to thin. Haugh units are calculated using both the egg weight and the height of the thick albumen. Standard Haugh unit values for different grades of eggs are follows: Grade AA is greater than 72 Haugh units, Grade A is between 60 and 72 Haugh units, and Grade B is less than 60 Haugh units. The USDA (United States Department of Agriculture) requires that all eggs for human consumption be graded both in terms of weight (minimum weight requirements for applicable size, Medium, Large and Extra-Large) and quality (Grade AA, Grade A, Grade B).
One of the primary difficulties presented with shell egg pasteurization is that eggs come in different sizes, weights and have different heat transfer characteristics. For example, the time in which an extra large egg is required to be submerged within a water bath at a given temperature for pasteurization (e.g. to achieve a 5 log reduction in salmonella) would likely partially denature the albumen or at least compromise the functionality of a medium sized egg. In addition to different egg size and quality, the starting temperature of the egg at the beginning of the pasteurization process must be taken into account as well. For this reason, it may be desirable to let refrigerated batches of eggs stand at room temperature or in a warming bath prior to pasteurization.
In prior art batch processing pasteurization equipment using a heated water bath, each batch contains many dozens of eggs typically arranged in flats and stacked one upon another, for example, as described in U.S. Pat. No. 6,113,961 which is also incorporated herein by reference. The design of the flats facilitates effective, even access of heated water to the eggs physically located in the middle of the batch. Pressurized air can be supplied through openings into the water bath to cause perturbation and facilitate effective heat transfer as also discussed in the U.S. Pat. No. 6,113,961. In one prior art system, each batch of eggs is held in a carrier that is supported by a gantry located above the water bath and is moved in three (3) stages through each of four (4) zones in the water bath. An advance motor moves the respective carriers sequentially from stage to stage and zone to zone at fixed time intervals.
FIG. 1 illustrates a prior art temperature control system 10 for a pasteurizer water bath. The system 10 includes a programmable logic control (PLC) 12 that controls the temperature within each of the zones 14 in the pasteurizer water bath. FIG. 1 schematically depicts the PLC 12 controlling the water temperature in one of the zones 14 in the water bath. Temperature sensors 16 are located within the water bath in each zone 14, and provide temperature signals to the PLC 12. Heating coils 18 are located in each zone 14 of the water bath. The PLC 12 controls the operation of a boiler 20 and a control valve 22 to provide heat to the respective heating coils 18 when required. The set temperature for the PLC 12 is different depending on the size of the eggs, e.g. medium sized eggs have a lower set temperature than large or extra large eggs. The level of air pressure and the motor advance rate are not controlled by the PLC 12, and are generally fixed and not changed after the system 10 has been installed and set up for operation. The system 10 also includes a water level sensor 24 that provides a signal to the PLC 12. When the water level in the water bath 14 falls below the sensor level 24, the PLC 12 opens valve 26 to add cold water to the water bath. The system 10 and the PLC 12, however, do not control the cold water valve 26 in response to the temperature sensor 16. In the prior art system 10, the PLC 12 is able to communicate with a computer 28 to allow an operator or supervisor to view data on the PLC 12, e.g., check alarm status to ensure that the system 10 is operating properly and that the temperature in any given zone has not drifted outside of a desired temperature range.
As mentioned, a batch of medium eggs weighs substantially less than a batch of large eggs or extra large eggs, and hence will have significantly lower thermal capacity. When a batch of eggs is introduced into the water bath, it immediately absorbs a large amount of energy because of the large temperature difference between the eggs and the water bath temperature. As the batch of eggs warms to or near the water bath temperature, the speed and the amount of heat transfer from the water bath to the eggs lessens. However, large and extra large eggs typically have more of an impact on the bath temperature in the initial zone than medium sized eggs, and the start temperature (e.g. refrigerated or room temperature) of the batch of eggs also has a significant impact on the temperature in the initial zone.
One object of the present invention is to provide the ability to pasteurize shell eggs not only at optimized bath temperatures, but also for optimized dwell times in the respective zones in the bath depending on egg size, weight and the starting temperature of the particular batches of eggs.
Certification of proper pasteurization requires verification checks on bath temperature and processing times to confirm that an approved pasteurization protocol (e.g. verified to meet FDA standards) has been employed and that equipment is performing in accordance with the protocol. While the prior art system allows the operator or supervisor to check the current status of the system and the temperature sensors via a connected computer 28, it does not provide data acquisition and reporting capabilities. Another object of the invention is to provide data acquisition and reporting capabilities in a manner that fosters thorough, convenient confirmation of batch compliance with approved pasteurization protocols.
Also, in the event that the pasteurization process falls out of compliance for one or more batches, it is important that these batches be removed from downstream processing and packaging. Another object of the invention is to provide an on-site alarm signal that indicates to system operators when a batch needs to be removed from the processing stream.